The phrase "a key note" is correct and usable in written English.
It is typically used to refer to an important point or theme, often in the context of a speech or presentation.
Example: "The speaker emphasized a key note about the importance of sustainability in modern business practices."
Alternatives: "a main point" or "a crucial aspect".
This is a key note for all keynote speakers.
The Medicine & Muse symposium also features a key note speaker.
TH: Colour was absolutely a key note, the leading stylistic structuring device in the entire way we approached the production.
Overall, acceptance is a key note in both books, but Go Set a Watchman manages to go further (after all we are talking about Harper Lee).
It was tricksy, tricked-out American sportswear, which is becoming something of a key note of New York fashion Week (hopefully, not a one-note key note).
May 9, 2013: Clarke Program Director Annelise Riles gave a key note lecture ("Market Collaboration") at the Canadian Society of Socio-cultural Anthropology Annual Meeting in Victoria, Canada.
Andrew Dickson, author of The Rough Guide to Shakespeare was a key-note speaker, there was a session led by directors and actors from the National theatre in bringing Shakespeare alive as well as workshops in sharing good practice.
Up to now deniability has been a key-note of Moscow's "ambiguous war" strategy in eastern Ukraine.
She graced the covers of magazines and TV shows, and spoke prophetically as a key-note-speaker at various technology conferences.
"Ours is a unique industry when it comes to mitigating climate change". Teresa Presas, Managing Director of CEPI (Confederation of European Paper Industries), will be a key-note speaker on Opportunities for Development at the XIII World Forestry Congress in Argentina.
Speech Rallies The Troops 8. (SBU) Clegg went into the spring conference shaken by the events of the previous two days, but managed to deliver a strong key note speech that went some way toward repairing the damage.
